I have a user who has a 8900, he connects to his mailbox via a BES.
He has several sub folders in his mailbox which are all showing on his Blackberry, he would like to hide/disable some of these folders as he does not need access to them on his Blackberry.
I have looked but can not find the option to do this, Is this possible ?

No, I don't believe you can have them on Outlook but not reflected on your BB. The BB is designed to mirror Outlook and provide all the functions of it. I've never seen anyone ask NOT to have them.

Not that I'm aware of either. He won't actually get any mail forwarded to those subfolders unless redirection is enabled for the desired subfolders anyway.